The present invention relates to polycomponent polymer blends of the ABS-type, having improved physical properties as compared with known ABS-type polyblend compositions. More particularly, the present invention relates to a polymer tri-blend of the ABS-type having improved elongation properties, flexibility properties, and impact strength, as compared with known ABS-type polymer blends of similar total rubber content.
As used herein, the term "ABS" refers to the monomers acrylonitrile, butadiene, and styrene, of which the instant polyblend compositions are comprised. As also used herein, the term "SAN copolymer" refers to a copolymer comprised of styrene and acrylonitrile monomers.
It is known in the prior art that different polymers may be blended together to provide a polyblend product having the desirable physical properties exhibited by the individual polymer components of the blend. It is also known in the prior art that a polymer composition having a particularly attractive combination of physical properties may be obtained by blending a styrene-acrylonitrile copolymer with one or more rubbery polymers, such as butadiene polymers and copolymers. Typical examples of such prior art polyblend compositions are described in U.S. Pat. Nos. 2,802,808; 4,009,226; and 4,009,227. U.S. Pat. No. 2,802,808 describes a polymer tri-blend comprising a styrene-acrylonitrile copolymer, a styrene-acrylonitrile-butadiene copolymer, and a butadiene polymer. Similarly, U.S. Pat. Nos. 4,009,226 and 4,009,227 describe polymer tri-blends of a styrene-acrylonitrile copolymer, a styrene-acrylonitrile-butadiene copolymer having a larger rubber particle size, and a styrene-acrylonitrile-butadiene copolymer having a smaller rubber particle size. U.S. Pat. No. 4,009,227 adds the additional requirement that the ratio of styrene to acrylonitrile in each of the polymer components of the polyblend of U.S. Pat. No. 4,009,226 must satisfy certain ratios.
While the aforementioned polyblends exhibit satisfactory physical properties in certain respects, the attainment of satisfactory impact strengths, elongation properties, and flexibility properties requires the use therein of an undesirably large amount of the rubbery butadiene polymer or copolymer. Since polybutadiene is a relatively expensive material, the large amounts of this material required in the prior art polyblends in order to achieve satisfactory physical properties results in an undesirably high priced thermoplastic material, the high price of which limits the commercial use of this material. Thus, while it is known in the prior art to blend a styrene-acrylonitrile (SAN) copolymer with a butadiene backbone polymer or copolymer, the prior art polyblends which exhibit satisfactory physical properties have proven relatively expensive, and therefore suitable for use in only a limited number of commercial applications.
There exists a great need in the art, therefore, for an inexpensive thermoplastic composition which exhibits high impact strengths, elongation values, flexibility properties, melt flow properties, and other desirable physical properties.